I know this is more of an engine question, but it's more of a drag racing engine question than a general engine question.

I know smokey yunic (sp) always said to cram the biggest rods you can in an engine. and bigger rods = more torque. I'm looking at eagle 4340 h beam rods, but should i go with 5.7", 6.0", or 6.25" rods? I've got 64cc heads that i'm planning on keeping and i'm planning on using je/ross/wiseco pistons with a dome to get to 10.5:1 cr. Does the rod length affect cr if i order pistons made for that length rod? are there going to be clearance problems running 6" rods in a 350 with a 350 crank? what kind of hp can a stock 350 crank hold up to? I'm plannin on 420hp n/a and 550+ w/no2. And lastly, what's the difference between pressed and full floating wrist pins?

I'm sorry i have so many questions, people in car magazines list off all the big components and why they're good but miss the little things.

 

Longer rods do not equal more torque. Longer rods increase piston dwell at TDC. They also have no affect on compression ratio since the stroke is controlled by the crankchaft. Unless you're going to be making 600+ HP with a SBC then stick to 5.7 or 6" rods. Exotic long rods create problems in stock engines. Extra clearance is required at the bottom of the cylinders and small base circle cams are usually required. A longer rod also moves the wrist pin higher into the piston. The SBC short deck height doesn't allow a very long rod before the wrist pin gets close to the compression rings.

Pressed pins are pressed into the con rods. The clearances are so close that the con rod and wrist pin don't move.

Floating pins have a couple of thousands of an inch clearance so the wrist pin slides in the con rod. The wrist pin is held in place by retaining rings in the piston. A floating pin piston is easier to remove if changes or modifications are needed.

 

Stephen, whats your position on the rod/stroke ratio? What do you think is the optimal ratio? I'm going for the 1.76 ratio, using a 6.125" rod in a 350. Isn't decreasing the rod angle at 90* crank rotation supposed to be better for the longevity of the engine?

 

I ran a 383 short rod stroker for 2 years. Running high 11's at 117 it failed because of cast pistons and stock rod bolts not because of the short rods.

It's always good to go to a longer rod but you must be aware of the internal clearances associated with them. They're not instant HP and a dyno pull would show little difference in performance.

High compression engines, 12:1 and over, would benifit more from the increased rod length since it would allow the piston to stay at TDC a little longer for the slower burning fuel to produce more energy.

My BBC buildup is going to a +.250" rod. The BBC deck height is very tall compared to a SBC so the wrist pin location in the piston isn't as bad. A longer rod also allows for a lighter piston. Lightweight pistons are better for a high reving race engine.

Smokey wasn't building street engines with his long rods. They were all designed as race engines.

 

So with all other parts of the engine being the same, and if cost wasn't an issue, which would you build? Would you stick with Chevrolet's stock rod/stroke ratio, or would you opt for a longer rod?